1. Field of the Invention
The present invention relates to a plasma display unit, and more particularly to an AC-discharge, memory-type plasma display unit.
2. Description of the Related Art
Plasma display units emit visible light to energize pixels by producing an electric discharge in a rare gas such as of Ne or Xe to generate ultraviolet radiation for exciting phosphors to emit visible light. The plasma display units display images in the form of a dot matrix, and are drawing attention as flat display units capable of emitting-light with high luminance.
CRTs (Cathode-Ray Tubes), which are a typical image display unit, have an appreciable depth that increases as the screen size increases. However, the depth of a plasma display unit does not increase even if its screen size increases.
LCD (Liquid Crystal Display) units have individual display cells, and their yield sharply drops when their screen size increases. However, the yield of plasma display units is not greatly reduced when their screen size increases because display cells are provided by points of intersection of vertical and horizontal electrodes.
Plasma display units include DC-discharge and AC-discharge types. The AC-discharge plasma display units have a dielectric protective film over the electrodes which are therefore not exposed to a discharge space. Consequently, the AC-discharge plasma display units have a much longer service life than the DC-discharge plasma display units whose electrodes are exposed.
The AC-discharge plasma display units are divided into refresh-type and memory-type plasma display units depending on how they are energized. The memory-type plasma display units produce wall charges using the dielectric on the electrodes, and generate an electric discharge by giving and receiving such wall charges.
More specifically, when a number of display cells in the display panel of a memory-type plasma display unit are successively scanned, wall charges are written in only those display cells which are to emit light according to image data. After the writing of the wall charges is completed, sustaining pulses are repeatedly applied to all the display cells, enabling only the display cells in which the wall charges are written to generate an electric discharge to emit light.
In such a memory-type plasma display unit, it is difficult to control the luminance of light by controlling the intensity of the electric discharge. Therefore, it is the general practice to control the number of times that a sustaining pulse is applied per display cell for thereby changing the visually perceived luminance to express gradations.
The AC-discharge plasma display units include surface-discharge AC-discharge plasma display units which have surface-discharge electrode pairs of scanning and sustaining electrodes placed in a plane, and facing-discharge AC-discharge plasma display units which produce an electric discharge between facing substrates. The surface-discharge AC-discharge plasma display units are expected as large-size, full-color flat display units because it is easier to develop electrostatic capacitance for forming wall charges, a memory margin is wider, phosphors are less degraded, and the emission efficiency is better.
One conventional AC-discharge, memory-type, surface-discharge plasma display unit will be described below with reference to FIGS. 1 through 3 of the accompanying drawings. For illustrative purposes, it is assumed that scanning and sustaining electrodes extend in a row direction, and data electrodes extend in a column direction.
As shown in FIG. 1, a plasma display unit 1 comprises a display panel 2 and a drive circuit 3. The display panel 2 has various electrodes connected to the drive circuit 3.
The display panel 2 includes a front transparent insulating substrate 15 and a rear insulating substrate 16. On the inner surface of the front transparent insulating substrate 15, there are disposed m surface-discharge electrodes pairs 10 comprising parallel scanning and sustaining electrodes 11, 12 as row electrodes parallel to the row direction and juxtaposed in the column direction.
On the inner surface of the rear insulating substrate 16, there are disposed n data electrodes 14 as column electrodes parallel to the column direction and juxtaposed in the row direction. A discharge space 13 filled with a rare gas including Xe is defined in the gap between the insulating substrates 15, 16.
Since the scanning and sustaining electrodes 11, 12 are positioned in front of light spots, they are usually made of an electrically conductive material that is highly light transmissive, such as ITO (Indium Tin Oxide). However, the material is not electrically conductive enough, so narrow trace electrodes 17, 18 of metal are placed on the scanning and sustaining electrodes 11, 12. A dielectric layer 19 and a protective layer 20 are successively placed on the trace electrodes 17, 18. The scanning and sustaining electrodes 11, 12 confront the discharge space 13 through the trace electrodes 17, 18, the dielectric layer 19, and the protective layer 20.
A dielectric layer 22 is disposed on the data electrodes 14 on the inner surface of the rear insulating substrate 16. Partitions 21 for blocking the propagation of electric discharges and spacing the insulating substrates 15, 16 from each other are disposed on the dielectric layer 22 and positioned between the data electrodes 14. A phosphor layer 23 is positioned on the surface of the dielectric,layer 22 and sides of adjacent two of the partitions 21.
The m surface-discharge electrodes pairs 10 and the n data electrodes 14 cross each other with the discharge space 13 interposed therebetween, providing mxc3x97n points of intersection successively arranged in the row and column directions as display cells 24 that serve as pixels for individually emitting light.
As shown in FIG. 1, the m scanning electrodes 11 have left ends connected respectively to m scanning wires 25, to which in scanning drivers 26 are individually connected. The m sustaining electrodes 12 have right ends connected in common to a single sustaining wire 27, to which a single sustaining driver 28 is connected.
To the n data electrodes 14, there are connected n data drivers 29, respectively. The above drives 26, 28, 29 jointly make up the drive circuit 3.
The AC-discharge, surface-discharge plasma display unit 1 is capable of displaying a desired image in the form of a dot matrix by individually controlling the mxc3x97n display cells 24 for light emission. A process of energizing the plasma display unit 1 will be described below with reference to FIG. 3.
In FIG. 3, xe2x80x9cWuxe2x80x9d represent sustaining pulses applied from the single sustaining driver 28 in common to the m sustaining electrodes 12, xe2x80x9cWs1-Wsmxe2x80x9d scanning pulses applied from the m scanning drivers 26 individually to the m scanning electrodes 11, and xe2x80x9cWdxe2x80x9d data pulses applied from the n data drivers 29 individually to the n data electrodes 14 with respect to those display cells 24 in which wall charges are to be written.
In a priming period A, preliminary discharge pulses Pp1, Pp2 are applied respectively to all the sustaining electrodes 12 and all the scanning electrodes 11, generating active particles and wall charges in the discharge space 13. Then, preliminary discharge erasing pulses Ppe are applied to the scanning electrodes 11 to erase excessive wall charges, developing a condition for stably writing wall charges.
In a scanning period B, the m scanning drivers 26 applies base pulses Pbw uniformly and also scanning pulses Pw at successively shifted times to the m scanning electrodes 11. In synchronism with these times, the n data drivers 29 apply data pulses Pd to certain data electrodes 14 which correspond to an image to be displayed.
Those display cells 24 where a pulse voltage in excess of a discharge threshold is applied to the scanning and data electrodes 11, 14 produce an electric discharge, writing wall charges into the surfaces of the dielectric layers 19, 20 on the scanning electrodes 11. As the wall charges grow, the effective voltage in the display cells 24 is lowered, storing substantially constant charges that are limited by the potential difference between the scanning pulses Pw and the data pulses Pd and the electrostatic capacitance of the stored region.
The base pulses Pbw are applied to the scanning electrodes 11 in the scanning period B in order to prevent the wall charges from being eliminated by an opposite electric discharge caused by the developed wall charges.
In a sustaining period C, sustaining pulses Pu, Ps are applied alternatively to all of the sustaining electrodes 12 and all of the scanning electrodes 11. In those display cells 24 where the wall charges are written, since the voltage of the wall charges is added to the sustaining pulses Pu, Ps, an electric discharge in excess of the discharge threshold is produced in the display cells 24 even though the voltage amplitude of the sustaining pulses Pu, Ps is low, and is sustained by the continued application of the sustaining pulses Pu, Ps. The first sustaining pulses Pu, Ps in the sustaining period C are set up such that the wall charges developed on the scanning electrodes 11 by the electric discharge are transferred to the sustaining electrodes 12.
As shown in FIG. 3, the time at which sustaining pulses Ps applied to the scanning electrodes 11 and the time at which the sustaining pulses Pu applied to the sustaining electrodes 12 are not the same as each other. Consequently, a state in which currents flow from the scanning electrodes 11 to the sustaining electrodes 12 as shown in FIG. 1, and a state (not shown) in which currents flow from the sustaining electrodes 12 to the scanning electrodes 11 occur alternately to each other.
With these states occurring alternately to each other, the direction of the sustaining pulses supplied to the surface-discharge electrodes pairs 10 is reversed. An electric discharge is produced in only the positions of the display cells 24 where the wall charges have been written, causing the phosphor layers 23 of those display cells 24 to emit light for thereby displaying an image.
In an erasing period D, the m scanning drivers 26 apply wide sustain erasing pulses Pe whose voltage gradually increases to the m scanning electrodes 11 for thereby stopping the above sustaining electric discharge, ending the display of the image. At this time, the display of one frame of image on the plasma display unit is completed. The above cycle of operation may be repeated to display a succession of images for thereby displaying a moving image.
For displaying a color image-on the plasma display unit 1, as shown in FIG. 4 of the accompanying drawings, data electrodes 14 may be arranged at a three-fold density, and three vertically long display cells 24 for R (Red), G (Green), and B (Blue) light emission may be combined to form a single pixel.
In the plasma display unit 1, it is easy to select energization and de-energization of the display cells 24, but it is difficult to adjust the luminance thereof in an analog fashion. Therefore, if a multi-gradation image is to be displayed on the plasma display unit 1, then a subfield process for combining a plurality of subfields with different emission luminance values to achieve a desired gradation is employed.
Specifically, since the display cells 24 of the plasma display unit 1 emit light when sustaining pulses are applied thereto while wall charges are being written therein, the subfield process controls the number of sustaining pulses to be applied to adjust the emission luminance values of the display cells 24 as emission times based on the integrating effect of visual perception.
For example, if a 256-gradation video signal is to be displayed in 8-bit binary gradations, then as shown in FIG. 5a of the accompanying drawings, it is possible to control a displayed gradation of a desired display cell 24 by energizing the display cell 24 with 8 subfields having respective numbers of sustaining pulses at ratios of xe2x80x9c1:2:4: . . . :128xe2x80x9d.
When the gradation level of a certain display cell 24 changes from 127 to 128, as shown in FIG. 5b of the accompanying drawings, a sustaining electric discharge is generated in a first frame by 7 subfields weighted by xe2x80x9c1, 2, . . . , 64xe2x80x9d such that the total weight is 127, and a sustaining electric discharge is generated in a second frame by only one subfield weighted by xe2x80x9c128xe2x80x9d.
In the above AC-discharge, memory-type, surface-discharge plasma display unit 1, scanning pulses are successively applied to all of the scanning electrodes 11, and data pulses are applied to certain data electrodes 14 to write wall charges in the positions of certain display cells 24. Sustaining pulses are applied the scanning electrodes 11 and the sustaining electrodes 12 to cause the display cells 24 where the wall charges have been written to emit light for thereby displaying an image in the form of a dot matrix.
In the plasma display unit 1, however, since images are displayed by the action of electric discharges, the wall charges and the sustaining pulses are of a high voltage of several hundred volts. When the sustaining pulses are applied, because currents of the sustaining pulses are supplied parallel to all the display cells 24 where light is to be emitted, the electric power required to display images on the plasma display unit 1 is very high. If there are many display cells 24 that are needed to emit light, then the plasma display unit 1 may develop an undue voltage drop, tending to bring about a light emission failure.
Basically, each of the display cells 24 of the plasma display unit 1 is capable of expressing two alternate values. The subfield process, however, makes it possible to display images in multiple gradations. When a multi-gradation moving image is displayed on the plasma display unit 1 according to the subfield process, the plasma display unit 1 is liable to suffer a fault known as moving-image false contouring.
As described above with reference to FIG. 5(b), sustaining pulses are concentrated in the former part of a frame for displaying the gradation level of 127, and sustaining pulses are concentrated in the latter part of a frame for displaying the gradation level of 128.
Therefore, a sustaining emission blank period is present between the frames where the gradation level changes from 127 to 128. Due to the sustaining emission blank period, the viewer visually recognizes the image as being instantaneously darker than the gradation level to be displayed.
When the gradation level changes from 128 to 127, as shown in FIG. 6 of the accompanying drawings, inasmuch as sustaining pulses are concentrated between the frames, the viewer visually recognizes the image as being instantaneously brighter than the gradation level to be displayed.
Therefore, when a relatively wide image area whose lightness varies smoothly, such as a cheek of a person, moves in the display screen, moving-image false contouring characterized by dark contours and bright contours appears in the smooth image area. If the image is a color image, then the moving-image false contouring is visually recognized as a color shift, resulting in a highly degraded display quality.
It is therefore an object of the present invention to provide a plasma display unit which prevents a display failure due to a voltage drop even if the plasma display unit has an increased screen size, can reduce electric field noise and magnetic noise, and reduce the effect of moving-image false contouring when gradation images are displayed according to the subfield process.
According to a first aspect of the present invention, there is provided a plasma display unit having a plurality of surface-discharge electrode pairs of scanning electrodes and sustaining electrodes extending parallel to a row direction and juxtaposed in a column direction, a plurality of data electrodes extending parallel to the column direction and juxtaposed in the row direction and defining pixels at positions where the data electrodes cross said surface-discharge electrode pairs, and a discharge space positioned in a gap between said data electrodes and said surface-discharge electrode pairs and containing a phosphor therein, the arrangement being such that scanning pulses are successively applied to said scanning electrodes and data pulses depending on an image are successively applied to said data electrodes to write wall charges in pixels corresponding to the image, and sustaining pulses flowing in alternately inverted directions are applied to said surface-discharge electrode pairs to cause an electric discharge in the positions of the pixels in which the wall charges are written, for thereby enabling the phosphor in said discharge space to emit light for thereby displaying a dot-matrix image, said plasma display unit comprising first set column writing means for applying data pulses of a predetermined polarity to said data electrodes in first set columns for writing the wall charges, second set column writing means for applying data pulses whose positive and negative polarities are opposite to the data pulses applied by said first set column writing means, to said data electrodes in second set columns other than said first set columns for writing the wall charges, first set row writing means for applying scanning pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said scanning electrodes in first set rows for writing the wall charges, and second set row writing means for applying scanning pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the scanning pulses applied by said first set row writing means, to said scanning electrodes in second set rows other than said first set rows for writing the wall charges.
For writing the wall charges, the first set column writing means applies data pulses of a predetermined polarity to said data electrodes in first set columns, and the second set column writing means applies data pulses whose positive and negative polarities are opposite to the data pulses applied by said first set column writing means, to said data electrodes in second set columns other than said first set columns. The first set row writing means applies scanning pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said scanning electrodes in first set rows, and the second set row writing means applies scanning pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the scanning pulses applied by said first set row writing means, to said scanning electrodes in second set rows other than said first set rows.
For example, if the data pulses applied to the data electrodes are of positive polarity in the first set columns and of negative polarity in the second set columns, the scanning pulses applied to the scanning electrodes in the first set rows are inverted between positive and negative polarities in the first and second states, and the scanning pulses applied to the scanning electrodes in the second set rows are inverted between negative and positive polarities in the first and second states, then wall charges are written into pixels at the points of intersection between the first set rows and the second set rows and pixels at the points of intersection between the second set columns and the first set rows in the first state, and wall charges are written into pixels at the points of intersection between the first set columns and the first set rows and pixels at the points of intersection between the second set columns and the second set rows in the second state.
Therefore, the pixels arranged vertically and horizontally in a two-dimensional matrix are alternately energized in a staggered grid pattern. The number of pixels which are simultaneously energized is half the number of pixels in the conventional plasma display unit. Therefore, it is possible to prevent a shortage of wall charges due to a voltage drop, so that images can be displayed in good quality even if the plasma display unit has an increased screen size.
According to a second aspect of the present invention, the plasma display unit comprises first set row writing means for applying scanning pulses of a predetermined polarity to said scanning electrodes in first set rows for writing the wall charges, second set row writing means for applying scanning pulses whose positive and negative polarities are opposite to the scanning pulses applied by said first set row writing means to said scanning electrodes in second set rows other than said first set rows for writing the wall charges, first set column writing means for applying data pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said data electrodes in first set columns for writing the wall charges, and second set column writing means for applying data pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the data pulses applied by said first set column writing means, to said data electrodes in second set columns other than said first set columns for writing the wall charges.
For writing the wall charges, the first set row writing means applies scanning pulses of a predetermined polarity to said scanning electrodes in first set rows, and the second set tow writing means applies scanning pulses whose positive and negative polarities are opposite to the scanning pulses applied by said first set row writing means to said scanning electrodes in second set rows other than said first set rows. The first set column writing means applies data pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said data electrodes in first set columns, and the second set column writing means applies data pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the data pulses applied by said first set column writing means, to said data electrodes in second set columns other than said first set columns.
For example, if the scanning pulses applied to the scanning electrodes are of positive polarity in the first set rows and of negative polarity in the second set rows, the data pulses applied to the data electrodes in the first set columns are inverted between positive and negative polarities in the first and second states, and the data pulses applied to the data electrodes in the second set columns are inverted between negative and positive polarities in the first and second states, then wall charges are written into pixels at the points of intersection between the first set rows and the second set columns and pixels at the points of intersection between the second set rows and the first set columns in the first state, and wall charges are written into pixels at the points of intersection between the first set rows and the first set columns and pixels at the points of intersection between the second set rows and the second set columns in the second state.
Therefore, the pixels arranged vertically and horizontally in a two-dimensional matrix are alternately energized in a staggered grid pattern. The number of pixels which are simultaneously energized is half the number of pixels in the conventional plasma display unit. Therefore, it is possible to prevent a shortage of wall charges due to a voltage drop, so that images can be displayed in good quality even if the plasma display unit has an increased screen size.
In the above plasma display unit, it is possible to simultaneously apply the scanning pulses from said first set row writing means and said second set row writing means.
Since the first set row writing means and said second set row writing means apply the scanning pulses to the scanning electrodes in the first set rows and the second set rows, two rows of pixels are energized at once even when the pixels are energized in rows. Because in each row the number of pixels that are energized is half, however, the number of pixels that are energized in rows is reduced to half, and images can be displayed at the same rate as with the conventional plasma display unit without increasing the processing burden for image data.
It is possible to simultaneously apply scanning pulses from said first set row writing means and said second set row writing means to a pair of said scanning electrodes in said first and second set rows which are spaced apart by a predetermined number of rows.
Since said first set row writing means and said second set row writing means simultaneously apply scanning pulses to a pair of said scanning electrodes in said first and second set rows, the writing of wall charges is not simultaneously carried out in two adjacent rows. Therefore, unwanted wall charges are prevented from being written in error into pixels due to the voltage of scanning pulses applied to adjacent rows, so that images of good quality can be displayed.
The plasma display unit may further comprise sustaining pulse applying means for applying sustaining pulses which flow in alternately inverted directions to said surface-discharge electrode pairs in said first set rows, and applying sustaining pulses which flow in alternately inverted directions, opposite to the sustaining pulses applied to said surface-discharge electrode pairs in said first set rows, to said surface-discharge electrode pairs in said second set rows.
Inasmuch as the sustaining pulse applying means applies sustaining pulses which flow in alternately inverted directions to said surface-discharge electrode pairs in said first set rows, and applies sustaining pulses which flow in alternately inverted directions, opposite to the sustaining pulses applied to said surface-discharge electrode pairs in said first set rows, to said surface-discharge electrode pairs in said second set rows, magnetic noises simultaneously generated in many surface-discharge electrode pairs due to the flow of sustaining pulses cancel out each other in the first set rows and the second set rows, reducing adverse effects on surrounding regions. The sustaining pulses are applied to the scanning electrodes and the sustaining electrodes of the surface-discharge electrode pairs. Since wires of the scanning electrodes are classified into the first set rows and the second set rows for connection to the first and second set row writing means, any complex wires needed for applying the sustaining pulses opposite directions to the surface-discharge electrode pairs in the first set rows and the second set rows can be minimized.
The plasma display unit may further comprise sustaining pulse applying means for applying a voltage which is alternately inverted between positive and negative polarities as sustaining pulses to flow in said surface-discharge electrode pairs to said scanning electrodes, and applying a voltage which is alternately inverted between positive and negative polarities in an opposite pattern to said sustaining electrodes.
The sustaining pulse applying means applies a voltage which is alternately inverted between positive and negative polarities as sustaining pulses to flow in said surface-discharge electrode pairs to said scanning electrodes, and applies a voltage which is alternately inverted between positive and negative polarities in an opposite pattern to said sustaining electrodes, for thereby supplying sustaining pulses to the surface-discharge electrode pairs. Since the voltage applied as sustaining pulses is of opposite polarities on the scanning electrodes and the sustaining electrodes, electric field noises generated in the scanning and sustaining elements of the surface-discharge electrode pairs cancel out each other upon application of the sustaining pulses of a high voltage, reducing adverse effects on surrounding regions.
The plasma display unit may further comprise a discharge accelerator disposed on at least a portion of a surface of each of said data electrodes for accelerating an electric discharge.
When data pulses of negative polarity are applied to the data electrodes, the data electrodes emit secondary electrons. Such secondary electron emission is blocked by the phosphor. The discharge accelerator disposed on at least the portion of the surface of each of said data electrodes accelerates an electric discharge from the data electrodes. Because wall charges can well be written even when data pulses of negative polarity are applied to the data electrodes, the plasma display unit can display images of good quality.
The discharge accelerator may comprise a layer of MgO.
Inasmuch as the discharge accelerator in the form of a layer of MgO is disposed on at least the portion of the surface of each of said data electrodes, the discharge accelerator is capable of accelerating an electric discharge due to its properties and well protecting the data electrodes.
The data electrodes may correspond to colors R, G, B in said first set columns and said second set columns.
As data pulses corresponding to the colors R, G, B are applied to the data electrodes in the first set columns and the second set columns, a number of pixels are energized according to R, G, B image data for displaying a full-color image. At this time, the first set column writing means simultaneously applies data pulses of a predetermined polarity to the data electrodes in the first set columns, and the second set column writing means simultaneously applies data pulses of a polarity opposite to the polarity of the data pulses applied to the data electrodes in the first set columns, to the data electrodes in the second set columns. In each of the set columns, since the data pulses applied to the data electrodes are of the same polarity, any potential difference between adjacent data electrodes due to the presence and absence of written wall charges is made small. Therefore, unwanted wall charges are prevented from being written in error into pixels due to the voltage for writing wall charges applied to adjacent rows, so that color images of good quality can be displayed.
According to a third aspect of the present. invention, a plasma display unit has a plurality of row electrodes extending parallel to a row direction and juxtaposed in a column direction, a plurality of column electrodes extending parallel to the column direction and juxtaposed in the row direction and defining pixels at positions where the row electrodes cross said column electrodes, and a discharge space positioned in a gap between said row electrodes and said column electrodes and containing a phosphor therein, the arrangement being such that drive pulses are successively applied to said row electrodes and said column electrodes, said drive pulses are increased to write wall charges into pixels corresponding to an image, and an electric discharge is generated in the positions of the pixels where the wall charges are written, for thereby enabling the phosphor in said discharge space to emit light for thereby displaying a dot-matrix image, said plasma display unit comprising first set column driving means for applying drive pulses of a predetermined polarity to said column electrodes in first set columns for writing the wall charges, second set column driving means for applying drive pulses whose positive and negative polarities are opposite to the drive pulses applied by said first set column driving means, to said column electrodes in second set columns other than said first set columns for writing the wall charges, first set row driving means for applying drive pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said row electrodes in first set rows for writing the wall charges, and second set row driving means for applying drive pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the drive pulses applied by said first set row driving means, to said row electrodes in second set rows other than said first set rows for writing the wall charges.
For writing the wall charges, the first set column driving means applies drive pulses of a predetermined polarity to said column electrodes in first set columns, and the second set column driving means applies drive pulses whose positive and negative polarities are opposite to the drive pulses applied by said first set column driving means, to said column electrodes in second set columns other than said first set columns for writing the wall charges. The first set row driving means applies drive pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said row electrodes in first set rows for writing the wall charges, and the second set row driving means applies drive pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the drive pulses applied by said first set row driving means, to said row electrodes in second set rows other than said first set rows for writing the wall charges.
For example, if the drive pulses applied to the column electrodes are of positive polarity in the first set columns and of negative polarity in the second set rows, the drive pulses applied to the row electrodes in the first set rows are inverted between positive and negative polarities in the first and second states, and the drive pulses applied to the row electrodes in the second set rows are inverted between negative and positive polarities in the first and second states, then pixels at the points of intersection between the first set columns and the second set rows and pixels at the points of intersection between the second set columns and the first set rows in the first state display an image, and pixels at the points of intersection between the first set columns and the first set rows and pixels at the points of intersection between the second set columns and the second set rows in the second state display an image.
Therefore, the pixels arranged vertically and horizontally in a two-dimensional matrix are alternately energized in a staggered grid pattern. The number of pixels which are simultaneously energized is half the number of pixels in the conventional plasma display unit. Therefore, it is possible to reduce the burden to drive the pixels to prevent a voltage drop, so that images can be displayed in good quality even if the plasma display unit has an increased screen size.
According to a fourth aspect of the present invention, a plasma display unit comprises first set column driving means for applying drive pulses of a predetermined polarity to said column electrodes in first set columns for writing the wall charges and enabling said phosphor to emit light, second set column driving means for applying drive pulses whose positive and negative polarities are opposite to the drive pulses applied by said first set column driving means, to said column electrodes in second set columns other than said first set columns for writing the wall charges and enabling said phosphor to emit light, first set row driving means for applying drive pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said row electrodes in first set rows for writing the wall charges and enabling said phosphor to emit light, and second set row driving means for applying drive pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the drive pulses applied by said first set row driving means, to said row electrodes in second set rows other than said first set rows for writing the wall charges and enabling said phosphor to emit light.
For writing the wall charges and enabling said phosphor to emit light, the first set column driving means applies drive pulses of a predetermined polarity to said column electrodes in first set columns, and the second set column driving means applies drive pulses whose positive and negative polarities are opposite to the drive pulses applied by said first set column driving means, to said column electrodes in second set columns other than said first set columns. The first set row driving means applies drive pulses which are inverted between positive and negative polarities in first and second states which occur alternately, to said row electrodes in first set rows, and the second set row driving means applies drive pulses which are inverted between positive and negative polarities in said first and second states in opposite relation to the polarities of the drive pulses applied by said first set row driving means, to said row electrodes in second set rows other than said first set rows.
For example, if the drive pulses applied to the column electrodes are of positive polarity in the first set columns and of negative polarity in the second set columns, the drive pulses applied to the row electrodes in the first set rows are inverted between positive and negative polarities in the first and second states, and the drive pulses applied to the row electrodes in the second set rows are inverted between negative and positive polarities in the first and second states, then pixels at the points of intersection between the first set columns and the second set rows and pixels at the points of intersection between the second set columns and the first set rows in the first state display an image, and pixels at the points of intersection between the first set columns and the first set rows and pixels at the points of intersection between the second set columns and the second set rows in the second state display an image.
Therefore, the pixels arranged vertically and horizontally in a two-dimensional matrix are alternately energized in a staggered grid pattern. The number of pixels which are simultaneously energized is half the number of pixels in the conventional plasma display unit. Therefore, it is possible to reduce the burden to drive the pixels to prevent a voltage drop, so that images can be displayed in good quality even if the plasma display unit has an increased screen size.
In a plasma display unit, a frame is divided into a plurality of subfields in advance, a plurality of display gradations produced by selecting the subfields are established in advance in each frame, image data with the display gradations established for pixels are successively input respectively for frames, subfields corresponding to the display gradations for the pixels of the successively input image data are selected to generate said data pulses, and the process of applying said scanning pulses, said data pulses, and then said sustaining pulses is carried out for each of said subfields, said subfields in said frame comprising two sets of subfields which are produced alternately, said two sets of subfields which are produced alternately being established as said first state and said second state, said subfields in the frame being arrayed in different patterns in said first state and said second state.
When image data with the display gradations established for pixels are successively input respectively for frames, subfields corresponding to the display gradations for the pixels of the successively input image data are selected to generate said data pulses, and the process of applying said scanning pulses, said data pulses, and then said sustaining pulses is carried out for each of said subfields. According to a subfield process, an image wherein display gradations of pixels are expressed equivalently by emission times is displayed. If a moving image is displayed by the subfield process, then moving-image false contouring occurs due to the arrangement of subfields in frames.
However, said subfields in said frame comprise two sets of subfields which are produced alternately, and said two sets of subfields which are produced alternately are established as said first state and said second state. Therefore, a number of pixels arranged vertically and horizontally in a two-dimensional matrix are alternately energized in a staggered grid pattern in subfields in the first and second states, so that moving-image false contouring occurs in different patterns in moving images in the first and second stages that are displayed in the staggered grid pattern. Accordingly, the moving-image false contouring is scattered and reduced to half, making it possible to display multi-gradation moving images of good quality.
The subfields as said first state may be arrayed in said frame such that allotted times thereof are successively increased, and said subfields as said second state may be arrayed in said frame such that allotted times thereof are successively decreased.
As time elapses in the frame, the subfields as the first state have their allotted times successively increased, and the subfields as the second state have their allotted times successively decreased. Even if the display gradations of a pair of pixels that are positioned adjacent to each other in the grid direction and alternately energized in the first and second stages are the same as each other, these pixels are energized and de-energized in opposite patterns. Therefore, moving-image false contouring can be canceled out, making it possible to display multi-gradation moving images of good quality.
The subfields as said first state and said second state may be arrayed such that allotted times thereof are increased toward a center of said frame.
As time elapses in the frame, the subfields as the first and second states have their allotted times successively increased and then successively decreased. The energization time in one of the first and second states is equivalent to the de-energization time in the other. If the subfields as the first and second states change similarly, then since the energization time is increased and decreased and the de-energization is increased and decreased in a corresponding manner, the energized and de-energized states are not concentrated in time, making it possible to display multi-gradation moving images of good quality.
The subfields as said first state and said second state may be arrayed such that allotted times thereof are decreased toward a center of said frame.
As time elapses in the frame, the subfields as the first and second states have their allotted times successively decreased and then successively increased. The energization time in one of the first and second states is equivalent to the de-energization time in the other. If the subfields as the first and second states change similarly, then since the energization time is increased and decreased and the de-energization is increased and decreased in a corresponding manner, the energized and de-energized states are not concentrated in time, making it possible to display multi-gradation moving images of good quality.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.